The present invention relates to a current limiting device utilizing a magnetic flux shielding characteristic of a superconductor and, more particularly, to an improvement of its current limiting performance.
If a current by, for example, short-circuiting in a power transmission and distribution system can be limited quickly, then it is possible to reduce the overcurrent margin of a transformer or the like connected to the system. This is advantageous in terms of design as well as economization. This also limits the flow of overcurrent to a short-circuiting portion on the consumer side to a fixed value or below, making it possible to suppress the spread of the trouble to the minimum and at the same time to prevent the trouble from affecting the power transmission and distribution system.
To this end, power transmission system utilizes means for minimizing damage from such a trouble by quickly cutting off the short-circuit current through use of a breaker, for example. Since the short-circuit current increases with an increase in the system capacity, however, the capacity of the breaker must also be increased accordingly.
It is technically difficult, however, to make the breaking current of the breaker to be greater than a value available at present. On this account, it is almost impossible to increase the present system capacity, making it difficult to meet growing demands.
In view of the above, some of the inventors of the subject application have proposed a current limiting device using a superconductor as a means whereby the breaking current is reduced rather than increased for increasing the system capacity.
Since the current value to be limited by such a current limiting device is a fixed value which depends on the superconductor used and the number of turns of the current limiting coil, however, there has been left unsolved a problem that it is necessary to fabricate a current limiting device which provides a required limited current value in accordance with the capacity of the system in which the current limiting device is used.